CHI3L1 and myeloid sarcoma: -CHI3L1 showed a strong expression in brain of MS patients, especially in astrocytes and microglial cells from white matter plaques; - CSF and serum CHI3L1 levels increased with the disease stage; -CIS patients with high CSF and serum CHI3L1 levels converted more rapidly to RRMS; -CSF CHI3L1/CHI3L2 ratio accurately discriminated PMS from RRMS.